The overall objective is to define the molecular mechanisms that regulate glycine biosynthesis and the flow of one carbon units in Salmonella typhimurium and Escherichia coli. The following approaches will be used to fulfill this objective: 1) Isolate regulatory mutants by selecting strains resistant to specific amino acid analogs. Use genetic techniques such as conjugation, transduction, and partial diploid analysis to locate the sites of these mutations relative to other markers on the E.coli and S. typhimurium linkage map and to study the effects of these mutations in trans. 2) Fuse the lac structural genes to the promoter controlling glyA gene expression. Use the techniques described for isolating mutations that alter the level of expression of the lac genes as a means of isolating mutants with altered control of the glycine pathway. 3) Perform physiological studies to determine the consequences of these mutations on regulation of the glycine and methionine pathways by measuring the levels and repressibility of enzymes representative of these pathways. Determine the number of different regulatory components involved in the control of serine transhydroxymethylase (glyA gene product). 4) Clone the glyA gene and its controlling segment from S.typhimurium and E.coli into plasmid vehicles using restriction enzyme and ligase technology. Use restriction mapping, an in vitro transcription system, and DNA sequencing techniques to determine the location and nucleotide sequence of the controlling segment for the glyA structural gene. Examine the responses of the control segment in vitro to the addition of the components found to be important for regulation during the physiological experiments.